Rendered Shadow is not sharp
Your light source is too big. I can't see what you are using, but if you are looking for unrealistic hard shadows (usually caused by artificial lighting), you need to get a smaller light source. If you are using an area lamp, get the size of it down and turn the strength up. You could also use a point lamp instead. A plane using an emission shader? Make it bigger. If you are looking for natural lighting, this is pretty accurate. Some more rendering samples will reveal the true shape of the shadow.